diff --git a/bitcoin/psbt.c b/bitcoin/psbt.c
index 7afb5a4fe..dfe4f8e53 100644
--- a/bitcoin/psbt.c
+++ b/bitcoin/psbt.c
@@ -641,6 +641,17 @@ void *psbt_get_lightning(const struct wally_map *map,
 	return item->value;
 }
 
+void psbt_set_lightning(const tal_t *ctx,
+			struct wally_map *map,
+			const u8 proprietary_type,
+			const void *value,
+			size_t val_len)
+{
+	u8 *key = psbt_make_key(NULL, proprietary_type, NULL);
+	map_replace(ctx, map, key, value, val_len);
+	tal_free(key);
+}
+
 void psbt_output_set_unknown(const tal_t *ctx,
 			     struct wally_psbt_output *out,
 			     const u8 *key,
diff --git a/bitcoin/psbt.h b/bitcoin/psbt.h
index 8d9eda2a0..b313cc028 100644
--- a/bitcoin/psbt.h
+++ b/bitcoin/psbt.h
@@ -220,6 +220,19 @@ void *psbt_get_lightning(const struct wally_map *map,
 			 const u8 proprietary_type,
 			 size_t *val_len);
 
+/* psbt_set_lightning - Set a propreitary lightning value on the given map
+ *
+ * @map - map of unknowns to set the value
+ * @proprietary_type - type no. to set
+ * @value - the value to be set
+ * @val_len - length of value
+ */
+void psbt_set_lightning(const tal_t *ctx,
+			struct wally_map *map,
+			const u8 proprietary_type,
+			const void *value,
+			size_t val_len);
+
 /* psbt_output_set_unknown - Set the given Key-Value in the psbt's output keymap
  *
  * @ctx - tal context for allocations